1. Field of the Invention
The present invention relates to a process for producing 2-chloroallyl thiocyanate of the formula (I) and 2-chloroallyl isothiocyanate of the formula (II).

2-Chloroallyl thiocyanate of the formula (I) is a known compound (see by way of example EP 0761649). It is also known that 2-chloroallyl thiocyanate of the formula (I) can be produced by reacting, in a diluent, a 2,3-dihalo-1-propene, preferably 2,3-dichloro-1-propene of the formula (III)
with a thiocyanate of the general formula (IV)M(SCN)n  (IV),in which                M is a metal cation or an ammonium groupand        n is from 1 to 4, as appropriate for the charge number of the cation.        
2. Description of Related Art
An example of a suitable diluent described for the known processes is acetonitrile (EP 446913; CN 1401646) or toluene, optionally with addition of a phase transfer catalyst (Shanghai Huagong 27 (2002) 25-27; J. Agric. Food Chem. 56 (2008) 10805-10810). However, the use of these diluents is disadvantageous for an industrial process. By way of example, the dilution of the starting materials can markedly reduce the reaction rate and thus prolong the reaction time required. The use of a diluent also unavoidably implies additional work-up steps. By way of example, distillation is required to remove the diluent, and care has to be taken here that the purity of the reclaimed diluent is sufficient to permit its return to the process. Otherwise there is a need for expensive disposal, which may cause pollution of the environment.
This also applies to the known use of water as diluent (EP 0761649; J. Agric. Food Chem. 52 (2004) 1918-1922). Here, the process is carried out in a mixture of two liquid phases (water and organic phase) in the presence of a phase transfer catalyst. There can then sometimes be considerable amounts of wastewater requiring disposal.
It is likewise known that the 2-chloroallyl thiocyanate of the formula (I) undergoes rearrangement at temperatures above room temperature to give 2-chloroallyl isothiocyanate of the formula (II) (EP 446913; EP 761649; J. Agric. Food Chem. 52 (2004) 1918-1922). When 2-chloroallyl thiocyanate of the formula (I) is obtained from 2,3-dichloro-1-propene of the formula (III) and from a thiocyanate of the formula (IV), mixtures of the compounds of the formulae (I) and (II) are therefore generally obtained. In industrial processes, this mixture is usually converted entirely to the 2-chloroallyl isothiocyanate of the formula (II) by heating, for example during distillative work-up. The overall process can accordingly be illustrated by the following diagram:
2-Chloroallyl isothiocyanate of the formula (II) is used by way of example as intermediate in producing plant-protection compositions (EP 446913).
There was therefore a continuing requirement for a further-improved process for producing 2-chloroallyl thiocyanate of the formula (I) and 2-chloroallyl isothiocyanate of the formula (II) under conditions that are advantageous in industry.